update error message for invalid distributed strategy (#945)

Summary:
Pull Request resolved: #945

Give examples of strings to use as strategies

Reviewed By: diego-urgell

Differential Revision: D65766329

fbshipit-source-id: e8c1182ef752816e52f1ff8a9d5e3ad500217f0b

torchtnt/utils/prepare_module.py

@@ -314,7 +314,7 @@ def prepare_module(
     if strategy:
         if not isinstance(strategy, str) and not isinstance(strategy, Strategy):
             raise ValueError(
-                f"Unknown strategy received: {strategy}. Expect either str or Strategy dataclass"
+                f"Unknown strategy received: {strategy}. Expect either str (one of 'ddp', 'fsdp', or 'noop') or Strategy dataclass"
             )
 
         if isinstance(strategy, str):